1. Technical Field of the Invention
The present invention relates to an improvement in a continuously variable transmission apparatus incorporating therein a toroidal-type continuously variable transmission for use as an automatic transmission apparatus for a car.
2. Description of the Related Art
As an automatic transmission apparatus for a car, use of such a toroidal-type continuously variable transmission as shown in FIG. 3 has been studied and enforced in part of the car industry. This is referred to as a toroidal-type continuously variable transmission of a double-cavity type, in which, on the peripheries of the two end portions of an input shaft 1, there are supported two input side disks 2, 2 through their associated ball splines 3, 3. Therefore, the two input side disks 2, 2 are respectively supported so as to be concentric with each other and can be rotated in synchronization with each other. Also, on the periphery of the middle portion of the input shaft 1, there is supported an output gear 4 in such a manner that it can be rotated with respect to the input shaft 1. And, two output side disks 5, 5 are respectively spline engaged with the two end portions of a cylindrical portion 9 disposed on the central portion of the output gear 4. Therefore, the two output side disks 5, 5 can be rotated in synchronization with the output gear 4.
Also, between the two sets of input side disks 2, 2 and output side disks 5, 5, there are interposed and held a plurality of (normally, two or three) power rollers 6, 6 in each set. These power rollers 6, 6 are rotatably supported on the inner surfaces of their associated trunnions 7, 7 through support shafts 8, 8 and a plurality of rolling bearings. The trunnions 7, 7 are respectively can be swung and shifted about their associated pair of pivot shafts which are disposed on the longitudinal-direction (in FIG. 3, the front-and-back-direction) two end portions of the trunnions 7, 7 in such a manner that they are concentric with each other in each set of trunnions 7, 7.
To operate the above-structured toroidal-type continuously variable transmission, using a drive shaft 10 connected to a power source such as an engine, one (in FIG. 3, the left-side) of the input-side disks 2 may be driven and rotated through such a pressing device 11 of a loading cam type as shown in FIG. 3 or an oil pressure type. As a result of this, the pair of input side disks 2, 2 supported on the two end portions of the input shaft 1 are rotated in synchronization with each other while they are being pushed in their mutually approaching directions. And, the rotation power of the two input side disks is transmitted to the output side disks 5, 5 through the power rollers 6, 6 and is then taken out from the output gear 4.
Now let us discuss a case in which the ratio of the rotation speed between the input shaft 1 and output gear 4. Firstly, to reduce the rotation speed between the input shaft 1 and output gear 4, the trunnions 7, 7 may be respectively -swung to their associated positions shown in FIG. 3. And, the peripheral surfaces of the respective power rollers 6, 6, as shown in FIG. 3, may be respectively contacted with the near-to-center portions of the inner surfaces of the input side disks 2, 2 and the near-to-outer-periphery portions of the inner surfaces of the output side disks 5, 5. On the other hand, to increase the rotation speed between the input shaft 1 and output gear 4, the trunnions 7, 7 may be respectively swung in the opposite direction to the direction shown in FIG. 3; and, the trunnions 7, 7 may be respectively inclined in such a manner that the peripheral surfaces of the respective power rollers 6, 6, reversely to the state shown in FIG. 3, can be respectively contacted with the near-to-outer-periphery portions of the inner surfaces of the input side disks 2, 2 and the near-to-center portions of the inner surfaces of the output side disks 5, 5. By the way, in case where the inclination angle of the trunnions 7, 7 is set in the intermediate inclination angle, between the input shaft 1 and output gear 4, there can be obtained an intermediate transmission ratio (speed ratio).
Further, conventionally, when incorporating the above-structured and—operatable into a continuously variable transmission for an actual car, there have been proposed various structures in which the toroidal-type continuously variable transmission is combined with a planetary gear mechanism to thereby provide a continuously variable transmission apparatus for a car, for example, structures as disclosed in U.S. Pat. No. 6,251,039 and JP-2778038. FIG. 4 shows, of the conventionally proposed continuously variable transmission apparatus, a continuously variable transmission apparatus disclosed in U.S. Pat. No. 6,251,039. This continuously variable transmission apparatus is composed of a combination of a toroidal-type continuously variable transmission 12 and a planetary-gear-type transmission 13. Of these transmissions, the toroidal-type continuously variable transmission 12 comprises an input shaft 1, a pair of input side disks 2, 2, an output side disk 5a, and a plurality of power rollers 6, 6. In the illustrated embodiment, the output side disk 5a has a structure in which the outer surfaces of a pair of output side disks are butted against each other to thereby form the two output side disks into an integral body.
Also, the planetary-gear-type transmission 13 includes a carrier 14 which is connected and fixed to the input shaft 1 and one (in FIG. 4, the right-side input side disk) of the two input side disks 2. And, on the diameter-direction intermediate portion of the carrier 14, there is rotatably supported a first transmission shaft 16 to the two end portions of which there are fixed two planetary gear elements 15a, 15b respectively. Also, a second transmission shaft 18, to the two end portions of which there are fixed two sun gears 17a, 17b respectively, is supported on the opposite side to the input shaft 1 with the carrier 14 between them in such a manner that it is concentric with the input shaft 1 and it can be rotated. And, the planetary gear elements 15a, 15b are respectively meshingly engaged with a sun gear 20 fixed to the leading end portion (in FIG. 4, the right end portion) of a hollow rotary shaft 19 having its base end portion connected to the output side disk 5a, or the sun gear 17a fixed to one end portion (in FIG. 4, the left end portion) of the second transmission shaft 18. Also, one (in FIG. 4, the left side) planetary gear element 15a is meshingly engaged, through another planetary gear element 21, with a ring gear 22 which is rotatably disposed on the periphery of the carrier 14.
On the other hand, another planetary gear elements 24a, 24b are rotatably supported on a second carrier 23 which is disposed on the periphery of the sun gear 17b fixed to the other end portion (in FIG. 4, the right end portion) of the second transmission shaft 18. By the way, the second carrier 23 is connected to the base end portion (in FIG. 4, the left end portion) of an output shaft 25 which is disposed concentrically with the input shaft 1 and second transmission shaft 18. Also, the planetary gear elements 24a, 24b are meshingly engaged with each other; and, one planetary gear element 24a is meshingly engaged with the sun gear 17b, whereas the other planetary gear element 24b is meshingly engaged with a second ring gear 26 which is rotatably disposed on the periphery of the second carrier 23. Further, the ring gear 22 and second carrier 23 can be engaged with and disengaged from each other by a low-speed clutch 27, while the second ring gear 26 and the fixed part of the continuously variable transmission apparatus such as a housing can be engaged with and disengaged from each other by a high-speed clutch 28.
In the case of the continuously variable transmission apparatus shown in FIG. 4, in a so called low speed mode state in which the low-speed clutch 27 is connected and the connection of the high-speed clutch 28 is cut off, the power of the input shaft 1 is transmitted through the ring gear 22 to the output shaft 25. And, by changing the transmission ratio of the toroidal-type continuously variable transmission 12, the transmission ratio of the whole of the continuously variable transmission apparatus, that is, the transmission ratio between the input shaft 1 and output shaft 25 can be changed. In such low speed mode state, the transmission ratio of the whole of the continuously variable transmission apparatus can be changed infinitely. That is, by controlling the transmission ratio of the toroidal-type continuously variable transmission 12, while the input shaft 1 is left rotating, the rotation state of the output shaft 25 can be changed between the forward and reversed rotation states thereof with a stop state between them.
By the way, during speed increasing operation in the above low speed mode state or during the constant speed running operation of a car, the torque passing through the toroidal-type continuously variable transmission 12 is transmitted from the input shaft 1 through the carrier 26, first transmission shaft 16, sun gear 20 and hollow rotation shaft 19 to the output side disk 5a, and is further applied from the outside disk 5a through the respective power rollers 6, 6 to the input side disks 2, 2. That is, the torque passing through the toroidal-type continuously variable transmission 12 during the speed accelerating or constant speed running operation circulate in a direction where the input side disks 2, 2 receive the torque from the power rollers 6, 6 respectively.
On the other hand, in a so called high speed mode state where the connection of the low-speed clutch 27 is cut off and the high-speed clutch 28 is connected, the power of the input shaft 1 is transmitted through the first and second transmission shafts 16, 18 to the output shaft 25. And, by changing the transmission ratio of the toroidal-type continuously variable transmission 12, the transmission ratio of the whole of the continuously variable transmission apparatus can be changed. In this case, as the transmission ratio of the toroidal-type continuously variable transmission 12 is increased, the transmission ratio of the whole of the continuously variable transmission apparatus can be increased.
By the way, during the speed increasing operation in such high speed mode state or constant speed running operation, the torque passing through the toroidal-type continuously variable transmission 12 is applied in a direction where the input side disks 2, 2 apply the torque to the power rollers 6, 6.
Although not shown, in JP-2,778,038, there is disclosed a continuously variable transmission apparatus structured such that a toroidal-type continuously variable transmission, two sets of planetary-gear-type transmissions, and four sets of clutches are combined together. According to such continuously variable transmission apparatus as disclosed in JP-2,778,038, by controlling the connection and disconnection of the four sets of clutches, there can be realized three kinds of modes on the advancing side and one kind of mode on the retreating side. And, not only the width of the transmission ratio on the advancing side can be increased but also, in the high-speed side two kinds of modes to be realized on the advancing side, the power passing through the toroidal-type continuously variable transmission can be controlled down to a low level, thereby being able to enhance the transmission efficiency of the whole of continuously variable transmission apparatus.
In the case of the above-mentioned conventional continuously variable transmission apparatus, since the toroidal-type continuously variable transmission and planetary-gear-type transmission are set coaxially with each other, the present continuously variable transmission apparatus becomes large in the axial-direction dimension thereof as a whole. Therefore, the above-mentioned conventional continuously variable transmission apparatus is not fit for a transmission for a front engine front drive car which has been widely spread mainly in the field of a small-sized car. In the case of the invention disclosed in JP-2778038, because it incorporates therein a so called single-cavity-type toroidal-type continuously variable transmission which includes an input side disk and an output side disk, the axial-direction dimension of the toroidal-type continuously variable transmission itself is short. However, as known widely, the single-cavity-type toroidal-type continuously variable transmission is poorer in transmission efficiency than the double-cavity-type toroidal-type continuously variable transmission shown in FIGS. 3 and 4. Therefore, when constituting a continuously variable transmission apparatus actually, as a toroidal-type continuously variable transmission, there is often used a double-cavity-type toroidal-type continuously variable transmission; however, in this case, as described above, the axial-direction dimension of the continuously variable transmission apparatus is inevitably increased. Also, in the case of the structure disclosed in JP-2778038, in addition to the input shaft of a toroidal-type continuously variable transmission, there are disposed two rotary shafts which are parallel to the input shaft. Due to this, the section area of the whole of the continuously variable transmission apparatus becomes large, which lowers the freedom of design thereof as a transmission for a small-sized car.
Further, in the case of the structure disclosed in JP-2778038, since there cannot be realized an infinite transmission ratio, in addition to the four sets of clutches, there is necessary a start mechanism such as a torque converter or an electromagnetic clutch. Due to this, the size of the whole of the continuously variable transmission apparatus becomes rather large, which makes it considerably difficult to employ the continuously variable transmission apparatus as a transmission for a small-sized FF car.